This invention relates to the making of glass. More particularly, it relates to an improved method of melting and refining glass in a vertically elongated electric melting furnace.
Vertically elongated glass melting furnaces having peripheral heating electrodes have been known in the art of glass making for many years. Illustrative of the state of the art are the following references: U.S. Pat. Nos. 2,186,178 to Ferguson, 2,263,549 to Peyches, 3,524,206 to Boettner et al., 3,583,861 to Preston, 3,725,588 to t'Serstevens, 3,742,111 to Pieper and 3,755,606 to Boettner et al. and in several foreign patents Swedish No. 80,130, Italian No. 298,239, German (W) No. 736,937 and French No. 1,305,805.
The patents of Peyches, Boettner et al. and Preston show sidemounted electrodes at a plurality of elevations to heat molten glass in the illustrated furnaces and to heat and melt glass batch materials floating on the molten glass by radiation and convection through the molten glass and conduction from it to the unmelted batch materials. In Boettner et al. U.S. Pat. No. 3,524,206 the heat energy applied to a furnace at any given elevation is greater than the heat energy applied at any lower elevation. In Preston the heat energy applied at a lower elevation of a furnace is sufficient to create an upward or countercirculation of glass particularly at the periphery of the furnace so that the downward flow of glass from an upper portion at a higher elevation of the furnace is nullified. The patent of Boettner et al. includes a scheme for increasing contact between unmelted batch and molten glass by encouraging the bottom surface of the floating glass batch to assume a conical shape similar to the depressed shape shown in U.S. Pat. No. 2,397,852 to Gentil. The German patent shows outwardly-tapered side walls near the top of a furnace, and the patent of Preston illustrates inwardly-tapered side walls near the bottom of a furnace.
While the glassmaking furnaces described in the prior art are all apparently useful for the melting of glass batch to prepare molten glass, the vertically elongated glassmaking furnaces of the past with their heating electrodes are not believed to be as thermally efficient as desired, nor to refine the molten glass sufficiently to provide for the making of high-quality flat glass. It is an objective now to provide an improved method of operation for vertically elongated, electrically heated glassmaking furnaces and to provide certain improvements to such furnaces themselves.